(1) Field of the Invention
This invention relates generally to digital cameras and relates more specifically to a position control of camera shutters driven by a linear motor.
(2) Description of the Prior Art
In photography, a shutter is a device that allows light to pass for a determined period of time, for the purpose of exposing photographic film or a light-sensitive electronic sensor to light to capture a permanent image of a scene.
As light travels through a lens opening (aperture), the shutter opens and closes in a timed fashion to determine how long the image sensor (“film”) gets exposed to a scene. The exposure time has a most important impact upon the quality of an image. Conventional film cameras are using usually mechanical shutters while digital cameras are often using digital shutters. It is a challenge for the designers of digital cameras to design a shutter mechanism for digital cameras, which can be exactly controlled.
The aperture of an optical system is the opening that determines the cone angle of a bundle of light rays that come to a focus in the image plane. The aperture determines how collimated the admitted rays are, which is of great importance for the appearance at the image plane. A narrow aperture will result in sharpness at the image plane, while a wide aperture will result in sharpness for light rays with the right focal length only. This means that a wide aperture results in an image that is sharp around what the lens is focusing on and blurred otherwise. The aperture also determines how many of the incoming rays are actually admitted and thus how much light that reaches the image plane, i.e. the narrower the aperture, the darker the image.
In addition, with the advancement of small portable terminals equipped with cameras having zoom functions and shutters there is a requirement of compact size shutters. Therefore there is a need of precise, compact size shutters, which are easily to be assembled.
Solutions dealing with camera shutters are described in the following patents or patent publications:
U.S. patent (U.S. Pat. No. 5,598,244 to Johansson) teaches a camera provided with means for effecting cyclic displacement of a mechanical system, such as a mirror mechanism or shutter mechanism, between two end positions. The means include spring means for biasing the system towards a neutral position or zone between the two end positions and drive means for ensuring that the system sequentially reaches said end positions.
U.S. patent (U.S. Pat. No. 6,157,100 to Mielke) discloses an electromagnetic drive for a focal-plane shutter of a camera having two light-excluding shutter curtains, each of the two shutter curtains being having its own electric drive motor, which is a linear motor constructed from permanent magnets and electromagnetic coils. The linear motor has at least two mutually aligned permanent magnets. The opposite pole faces of the magnets have the same polarity. A soft-magnetic disk is disposed between the permanent magnets. A soft-iron casing encloses the magnets and the soft-magnetic disk with an annular gap therebetween. A coil former is displaceably mounted in the annular gap such that it can exert an operating stroke between two stops. The coil former has a drive element for transferring the axial displacement of the coil former to the assigned shutter curtain.
U.S. Patent Publication (US 2007/0110433 to Masahiko) describes a shutter driving apparatus for a camera module having a shutter driving section constructed to slidingly move shutter blades provided to a camera lens module in both sideward directions to thereby open and close a lens opening. The shutter driving apparatus comprises a lens housing; a pair of shutter blades provided to the lens housing to be slidingly moved in a lengthwise direction of the lens housing to thereby open and close a lens opening of the camera lens module; and a pair of shutter driving sections respectively connected to the shutter blades via rotation links and each being configured for creating a pair of electromagnetically-opposite electromagnet poles and having a permanent magnet positioned between the poles such that a permanent magnet with at least one of the poles and connected to the rotation link is rotated due to a magnetic field created as current is applied to the electromagnet, to slidingly move an associated shutter blade.
U.S. Patent Publication (US 2007/0110433 to Masahiko) describes a shutter driving apparatus for a camera module having a shutter driving section constructed to slidingly move shutter blades provided to a camera lens module in both sideward directions to thereby open and close a lens opening. The shutter driving apparatus comprises a lens housing; a pair of shutter blades provided to the lens housing to be slidingly moved in a lengthwise direction of the lens housing to thereby open and close a lens opening of the camera lens module; and a pair of shutter driving sections respectively connected to the shutter blades via rotation links and each being configured for creating a pair of electromagnetically-opposite electromagnet poles and having a permanent magnet positioned between the poles such that a permanent magnet with at least one of the poles and connected to the rotation link is rotated due to a magnetic field created as current is applied to the electromagnet, to slidingly move an associated shutter blade.